The perl-base package must provide
perlapi-abiname for all released package versions it is
compatible with. The choice of abiname is arbitrary, but if it
differs from $Config{version}[1], it must be specified in $Config{debian_abi}.

2.2 Base Package

In order to provide a minimal installation of Perl for use by applications
without requiring the whole of Perl to be installed, the perl-base
package contains the binary and a basic set of modules.

As Perl has been part of the essential set for some time and is used without
dependencies by such things as package maintainer scripts,
perl-base must be priority required and marked as
essential.

Note that the perl-base package is intended only to provide for
exceptional circumstances and the contents may change. In general, only
packages which form part of the base system should use only the facilities of
perl-base rather than declaring a dependency on perl.

2.3 Module Path

Perl searches three different locations for modules, referred to in this
document as core in which modules distributed with Perl are
installed, vendor for packaged modules and site for
modules installed by the local administrator.

The module search path (@INC) in the Debian packages has been
ordered to include these locations in the following order:

These locations, particularly $Config{sitearch}, may change if the
binary interface between the Perl interpreter and compiled modules has to be
changed in an incompatible way without a change in version. While
this will only be done as a last resort, packages should use
$Config{sitelib} and $Config{sitearch}, not hardcode
the current locations.[2]